High frequency magnetron amplifier



Nov. l, 1938. E' G. LINDER Filed Dec. 31, 1935 HIGH FREQUENCY MAGNETRONAMPLIFIER Patented Nov. 1, 1938 UNITED STATES HIGH FREQUENCY MAGNETRON 1AMPLI- FIER Ernest G. Linder, Philadelphia, Pa., assignor` to RadioCorporation of America, a corporation of Delaware Application December31, 1935, Serial No. 56,890 i i 12 Claims.

My invention relatesV to amplifiers for high frequency currents. Morespecifically my invention is a push pull magnetron amplifier fo-ramplifying currents at ultra high frequencies.

Amplification of ultra high frequency currents with conventional typesof thermionic tubes oiiers numerous difliculties. These diiiculties areprimarily the result of the interelectrode capacities of the tubes. Myinvention contemplates the use of magnetron tubes ink which the electronpath is varied to effect amplication.

One of the objects of my invention is to amplify ultra high frequencycurrents by varying the electron path within a magnetron.

Another object is found in the means for effecting push pullamplification of ultra high frequenCy currents.

A further object is the design of a magnetron amplier having fourpositively biased electrodesl which are operated as oppositely arrangedpairs.

Additional objects will appear in the accom-k panying specification andappended claims.

An understanding of my invention `may best be had by referring to theaccompanying drawing in which,

Figure I is a schematic drawing `representing a magnetron embodying onearrangement of my invention, Y

Fig. Ia is a perspective viewof the electrodes of Fig. I,

Fig. II is a schematiccircuit 4diagram showing an embodiment of myinvention,

Fig. III is a schematicfillustrationv of a suitable circuit for pushpull amplification at ultra high frequencies,

Fig. IV is drawing used to illustrate themode of operation of themagnetron amplifier of my invention operating near the cut-off point,andFig. V is a graph or characteristic curve illustrating the relationbetween input voltages and output currents of a push pull magnetronampliiier.

In Fig. I within an evacuated envelope I are l arranged three pairs oflead wires. .One of these pairs 3-5 support a lament 1. The second pairof lead wires 9|| support a pair of4 cylindrical shape anodes |3-I 5.The remaining pair of wires |1|9 support a second pair of cylindricalshape electrodes 2|23.

These anodes are preferably madefrom a cylinder which has been dividedinto sections each having an angular Width equal to slightly less than aquadrant. These sections, by way of eX- ample, may have alengthabouttwice that of their width. 'I'he space between the cylindrical velope tovmaintain the filament and anode eleotrodes in their'proper positions.

The operation of Aa magnetron contemplates a magnetic field whose linesof force are substantially parallel with the axis of the anodes. Thisfield may be generated by an electromagnet Whose magnetic core 25 may beenergized by a suitable eld Winding 2l. T'he magnetic iield maybe variedby adjustments of the magnetizing currents.

Aperspective View of the electrodes is presented in Fig. Ia.' In thisfigure and throughout the specification, similar parts of the severalIgures will be represented by similar reference numerals. In FiglIa, themagnetic field and evacuated envelope `are omitted for simplicity ofillustration.

In Fig. II the anodes I3-'l 5 have been connected through thelead wires9-l I to a tunable tank circuit 29.y This circuit is composed of avariable capacitor 3| and an inductor 33. The inductor 33 is coupledtothe secondary 35 of an input circuit. The input circuit may be anantenna or thetank circuit 29 may serve as the antenna collectorcircuit.

The filament or cathode 1 is energized by a battery `not illustrated. Abiasing battery 3l has` its negative terminal'connected toA cathode andits positive terminal is connected to a point intermediate the ends ofinductor 33. This intermediate point is preferably the center of theinductor.

' The anodes 2I,-23 are connected through the lead wires I'l-'l9 to atunable output tank circuit 39. Thetank circuit is composed of aVariable capacitor 4I and an inductor 43. A tap is made at the centeriofthe inductor 43. This tap is connected vto. the positive terminal of abias battery 45. The negative terminal of the bias battery 45 isconnected to the filament l. The tank circuit 39 is coupled to an outputcircuit represented by the inductor 41. The output circuit mayY includeadditional amplifiers, detectors, or nienke.` s A 1 y L In Apractice thecapacitor 3 land inductor 33, or the capacitor and inductor 43, .are notseparate elements. One preferred form is to make a tank circuit asillustrated in Fig. III. In this ligure the lead wires 9-I I are slippedwithin a U shape tubular member 49. The electrical length of the circuitmay be adjusted by sliding the U shape member 49 on the lead wires 9-II. The wires and the U shape member1 have both capacitance andinductance whichis sufficient to tune the tank circuit throughout arange of ultra high frequencies. A similar U shape member 5I is adjustedon lead wires I'I-I9.

Biasing batteries 53-55 are respectively connected to the centers of theU shape members 49-5I. 'Ihe potential of the two batteries may beadjusted to obtain optimum amplication. In general the bias applied tothe input electrodes is less positive than the bias of the outputelectrodes. The negative terminals of these biasing batteries areconnected to the cathode 1. In Figs. 1I and III the magnetic fields havebeen illustrated by a circle and an appropriate legend to simplify thedrawing. It should be understood that magnetic fields are employed ineach case. Likewise positively charged end plates may` be used toestablish a suitable electrostatic iield with a component of its linesof force parallel to the cathode or filament I. The magnetic iields areused with the magnetrons employing end plates.`

Having described the magnetron tube and associated circuits, I shall nowexplain the operation of the amplier, without limiting my invention tothe precise theory set forth. In Figure IV the positively biasedelectrodes are represented as I3, I5, 2| and 23. In the absence of amagnetic field, electrons emitted from the cathode 'I will normally movein a straight line path from the cathode 'I to the positive electrodesI3, I5, 2l and 23. If, however, a magnetic ield is applied,`whose linesof force are perpendicular to the plane of the paper, the electronsemitted from the cathode 'I will traverse curvilinear paths such asrepresented by 51. The magnetic eld-and if end plates are used, theelectrostatic fieldand the biasing potentials are each adjusted vuntil acritical cutoff characteristic is reached ork exceeded.

At or beyond the critical Value the electron paths near the anodes arealmost tangent to the anodes. Under this condition, if a radio frequencycurrent is set up in the input tankcircuit, the flow of current in thetank circuit will lalternately apply positive charges to one anode andnegative charges to the other anode, said anodes being connected to thecircuit. The potential difference arising from these charges willincrease the number of electrons flowing to one of the output anodes anddecrease the number flowing to the other output anode.

The increased number of electrons arises from the increase in the forceacting on electrons leaving the cathode 'I and moving toward the morepositive of the input quadrants I3. Due to the increased force, theelectron velocity is increased. Since the magnetic field is constant itwill have less effect on the electrons moving at higher velocity and thepaths described by the electrons become of greater radius whereby largernumbers of electrons impinge on the output quadrant 23 because smallernumbers of electrons are tangent to the electrode 23.

Conversely, for the more negative, or less positive input electrode I5,the velocity of approaching electrons is decreased, the paths becomesmaller in radius, and fewer electrons impinge upon the output quadrant2i. When the input currents reverse in sign, the above described' actiontakes place between oppositely arranged pairs of electrodes; i. e.,electrode I5 takes the place of electrode I3, and electrode 2I takes theplace of electrode 23. The simultaneous increased and decreased electronflow is equivalent to push pull operation.

These results are obtained when the electron revolves around the cathodethrough an angle of not less than 0 or more than 180`0 as measured fromthe point of emission of said electron and to the point at which saidelectron impinges on one of said anodes. The required angular path isobtained by the design of the anode radius, the cathode radius, and thenormal operating space charge. The limits of angular rotation of theelectron path are not critical. I have found that magnetrons whosecathode radius is small with respect to the anode radius, and whosespace charge effect is negligible, will have electron paths Whose rangleof rotation falls within the prescribed limits. If magnetic elds greatlyexceeding the lcritical cut-off value are employed, the exact pathfollowed by the electrons will differ from the curve 51 Aof Fig. IV butthe net angular rotation of the path about the cathode will be withinthe prescribed limits.

The characteristic curves of input Vvoltage plotted against outputcurrents appear in Fig. V. If the operation is maintained between thepoints a and b on the curve c by proper adjustment of the magneticfield, the amplification is substantially linear.

It is evident that when the quadrants are of equal shape and size, andare symmetrically arranged, as shown in the drawing, the capacitybetween adjacent quadrants Will be uniform. Since alternate oppositelydisposed pairs rare connected in push-pull, equal and oppositely phasedvoltages will be induced in each output quadrant-by the two inputquadrants. Consequently, the net result is a Ycomplete neutralization ofthe effect of interelectrode capacity between input and outputelectrodes.'

'Ihe foregoing specification and drawing are merely illustrative of myinvention. Numerous modications Within the scope of my invention willoccur to those skilled in the art. It should be understood that myinvention is only limited as required by the prior art and appendedclaims.

I claim as my invention:

1. A magnetron amplifier having a cathode and four anodes; said anodesbeing symmetricallyarranged about said cathode, substantially parallelthereto, and separated from each other; an input circuit connected to apair of said anodes oppositely disposed about said cathode; .an outputcircuit connected to the remaining oppositely dis- Y posed pair ofanodes; and a magnetic field whose lines'of force are substantiallyparallel with said cathode.

2. A magnetron amplifier having a cathode and four anodes; said anodesbeing symmetrically arrangedabout said cathode, substantially parallelthereto,'and separated from each other; an input circuit connected toapair of said anodes oppositely disposed about said cathode; an outputcircuit connected to the remaining oppositely disposed pair of anodes; amagnetic field whose lines of force are substantially parallel with saidcathode, and means for positively biasing at least one of said pair ofanodes withrespect to said cathode.

3. In a device of the character. of claim 2, a pair of end plates whoseplanes 'are substantially perpendicular to said cathode, and means forbiasing said end plates positively with respect to said cathode.

4. A magnetron amplier having a cathode and four anodes; said anodesbeing symmetrically arranged about said cathode, substantially parallelthereto, and separated from each other; an input circuit connected to apair of said anodes oppositely disposed about said cathode; an outputcircuit connected to the remaining oppositely disposed pair of anodes; amagnetic field whose lines of force are substantially parallel with saidcathode and means for applying positive potentials to said pairs ofanodes with respect to said cathode.

5. An ultra high frequency amplier comprising an evacuated envelope; anelectron emitting cathode, four electrodes having curved surfaces, saidsurfaces being slightly less than 90 in width, concentrically disposedabout said cathode and within said envelope; an input circuit connectedto two oppositely disposed electrodes; an output circuit connected tothe remaining electrodes; means for biasing said electrodes positivelywith respect to said cathode; and means for causing electrons to followcurvilinear paths as the electrons travel from the cathode toward saidelectrodes.

6. An ultra high frequency amplifier comprising an evacuated envelope;an electron emitting cathode, four anodes of partial cylindrical shape,each separated from the other by spaces equal to angles of andconcentrically disposed about said cathode and within said envelope; aninput circuit connected to an oppositely disposed pair of said anodes;means revolving electrons about said cathode through an angle of morethan 0 and less than 180-0; and means including said anodes forincreasing the number of electrons impinging on one anode of the otherof said pair of anodes and for decreasing the number of electronsimpinging on the anode oppositely disposed to said last `mentioned anodewhereby the numbers of electrons reaching said anodes may berespectively in-,

creased and decreased to effect amplification of currents applied tosaid input circuit.

7. In a device of the character of claim 6 a tunable input circuitconnected in push-pull relation to two of said anodes, and a tunableoutput circuit connected in push-pull relation to the remaining twoanodes.

8. In a high frequency amplier circuit, an electron discharge tubehaving a cathode and a plurality of pairs of separate anodes, saidanodes being of partial cylindrical shape and concentrically arranged toform .a cylinder about said cathode, the anodes of each pair beingdiametrically opposed, means for producing a magnetic fieldsubstantially coaxial with respect to the system of said cathode andsaid anodes, means for applying to one pair of oppositely disposedanodes a direct current potential which is positive with respect to thepotential of said cathode, means for applying to a second pair of saidanodes a direct current potential which is positive with respect to thepotential of the first said anodes, means for impressing an alternatingpotential in a push-pull manner upon the rst said anodes with respect tosaid cathode, thereby to provide, in cooperation with the magnetic eld,a control of the electronic emission from said cathode, and meansincluding the more positively charged anodes for deriving amplifiedalternating output currents the frequency of which is determined by saidcon-- ling alternating voltage to two opposite anode segments thereby tocontrol the distribution of electronic flow radially from said cathode,means for producing a magnetic field in the region of said flow andhaving lines of force lying at an angle which approaches 90 with respectto the direction of said electronic flow and means including two otheroppositely disposed anode segments charged to a more positive potentialthan that of the first said anode segments for deriving a useful ampliedalternating current the frequency characteristics of which aredetermined by those of said controlling alternating voltage acting uponsaid electronic flow.

10. In an alternating current amplifying device, an electron dischargetube having an electron emitting axial cathode and a plurality of anodesof equal size arranged in opposite pairs the surfaces of which havepartial cylindrical form and are equi-distant from the axis of saidcathode, means for producing a magnetic eld which is substantiallycoaxial with said cathode, means for polarizing one pair of anodespositively with respect to said cathode and a second pair of anodespositively with respect to the first pair, means for impressing in apush-pull manner upon the iirst pair of anodes an alternating controlvoltage, and means includingan output circuit connected in .a push-pullmanner to the anodes of said'second pair for deriving a useful amplifiedalternating current.

11. The method of amplifying alternating currents in an electrondischarge tube having a heated cathode an-d a plurality of anodes ofpartial cylindrical shape, the surfaces of which are equi-distant fromsaid cathode and positively charged with respect thereto which consistsin producing a flow of electrons within the region surrounded by Saidanodes, controlling the distribution of said ow to one pair Aof saidanodes in dependence upon alternatio-ns of input energy applied in apush-pull manner to the anodes of another pair, and deflecting said owaway from the second said pair of anodes and toward said first pair independence upon the strength of a magnetic eld in which said anodes andsaid cathode are immersed.

12. A high frequency amplifier circuit cornprising an electron dischargetube having a cathode and a plurality o-f diametrically opposed anodesof partial cylindrical shape, the surfaces of which are equi-distantfrom said cathode, an input circuit connected between the cathode andone pair of opposed anodes, an output circuit connected between thecathode and a second pair of opposed anodes, and a source of magneticeld excitation arranged to be eifective in the electron discharge zoneof said tube.

ERNEST G. LINDER.

